U.S. patent number 6,623,131 [Application Number 10/217,546] was granted by the patent office on 2003-09-23 for reflective reading optical system.
This patent grant is currently assigned to Minolta Co., Ltd. Invention is credited to Makoto Ooki.
United States Patent |
6,623,131 |
Ooki |
September 23, 2003 |
**Please see images for:
( Certificate of Correction ) ** |
Reflective reading optical system
Abstract
A reading optical system that forms the image of the original
document on a one-dimensional imaging element, such system
comprising multiple reflective surfaces only, wherein at least one
of such surfaces is a free-form surface that has a symmetrical
surface relative to the main scanning direction and no symmetrical
surface relative to the sub scanning direction. Where the light
beam that passes through the center of the original document and
the center of the aperture is deemed the axial main light beam, the
path of the axial main light beam that strikes the first reflective
surface extends along the Z-axis, the length of the one-dimensional
imaging element extends along the Y-axis, and the X-axis extends
perpendicular to the Y-axis and the Z-axis, each reflective surface
is arranged such that it is tilted relative to the Y-axis.
Inventors: |
Ooki; Makoto (Toyokawa,
JP) |
Assignee: |
Minolta Co., Ltd (Osaka,
JP)
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Family
ID: |
19077593 |
Appl.
No.: |
10/217,546 |
Filed: |
August 14, 2002 |
Foreign Application Priority Data
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Aug 20, 2001 [JP] |
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2001-248436 |
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Current U.S.
Class: |
359/857; 359/856;
359/858; 359/861 |
Current CPC
Class: |
G02B
17/0642 (20130101) |
Current International
Class: |
G02B
17/06 (20060101); G02B 17/00 (20060101); G02B
007/182 () |
Field of
Search: |
;359/857,856,858,861,862
;250/201.5,204 ;369/44,45,46 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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11-023971 |
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Jan 1999 |
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JP |
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2000-275557 |
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Oct 2000 |
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JP |
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Primary Examiner: Sikder; Mohammad
Attorney, Agent or Firm: Morrison & Foerster LLP
Claims
What is claimed is:
1. An reading optical system that forms an image of an original
document on an one-dimensional imaging element, comprising:
multiple reflective surfaces only as optical surfaces with a focal
power, wherein at least one of the reflective surfaces is a
free-form surface which has a symmetrical surface relative to a
main scanning direction and has no symmetrical surface relative to
a sub scanning direction, and wherein each reflective surface is
arranged such that they are tilted relative to Y-axis, wherein
Z-axis extends along an incident light beam, which is the axial
main light beam that passes through a center of the original
document and a center of an aperture and strikes a first reflective
surface, the Y-axis extends along length of the one-dimensional
imaging element, and X-axis extends perpendicular to the Y-axis and
the Z-axis.
2. The reading optical system an claimed in claim 1, further
comprising: an aperture which exists between the first reflective
surface and a last reflective surface struck by the axial main
light beam.
3. The reading optical system an claimed in claim 2, wherein the
aperture is constructed integrally with the reflective surface.
4. The reading optical system an claimed in claim 2, wherein a
relationship expressed by a condition SY>SX is satisfied,
wherein SY is length of the aperture extending in the main scanning
direction, and SX is length thereof extending in the sub scanning
direction.
5. The reading optical system an claimed in claim 1, wherein a path
of the axial main light beam that first strikes the reflective
surface and a path of the axial main light beam that strikes the
imaging element are essentially perpendicular to each other on X-Z
cross-section.
Description
The present application claims priority to Japanese Patent
Application No. 2001-248436 filed Aug. 20, 2001, the entire content
of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflective reading optical
system, and more particularly, to a reflective reading optical
system suitable for an image reading apparatus (particularly a
digital copying machine, a facsimile or a scanner) equipped with a
one-dimensional imaging element such as a line CCD (charge coupled
device), for example.
2. Description of the Related Art
The optical surfaces having a focal power in the multi-beam type
scanning optical system proposed by Japanese Laid-Open Patent
Application 2000-275557 all consist of reflective surfaces. In this
construction, the increase in the width of the beam along the image
height due to positional offsetting for each beam is eliminated via
the reflective surfaces. An imaging optical system using reflective
surfaces is also known. For example, Japanese Laid-Open Patent
Application H11-23971 proposes a device that includes both
reflective and transmitting surfaces. However, because the device
disclosed in this laid-open patent application is used in order to
obtain two-dimensional images, correction of distortion is not
adequate. By contrast, adequate distortion correction is possible
in a reading optical system used to obtain one-dimensional images,
and a device using reflective surfaces is also known.
However, because a light source having a wide wavelength range is
used in an image reading apparatus, if a transmitting surface
having a focal power is included in the reading optical system, a
reduction in contrast caused by color aberration is unavoidable. In
addition, if multiple reflective surfaces are to be used in a
reading optical system, the reflective surfaces must be decentered,
and as a result of non-symmetricity of light beam positions in the
decenter cross-section, the problem arises that aberration
correction becomes difficult.
SUMMARY OF THE INVENTION
A main object of the present invention is to provide a reflective
reading optical system by which high contrast is obtained even if
the light source has a wide wavelength range, and by which
aberrations are well-corrected even where the reflective surfaces
are decentered.
In order to attain the above object, the reflective reading optical
system of the present invention is a reflective reading optical
system that forms the image of the original document on an
one-dimensional imaging element, such optical system having as
optical surfaces with a focal power multiple reflective surfaces
only, wherein at least one of such surfaces is a free-form surface
that has a symmetrical surface relative to the main scanning
direction and has no symmetrical surface relative to the sub
scanning direction, and wherein each reflective surface is arranged
such that they are tilted relative to the Y-axis.
Here, the Z-axis extends along the incident light beam, which is
the axial main light beam that passes through the center of the
original document and the center of the aperture and strikes the
first reflective surface. The Y-axis extends along the length of
the one-dimensional imaging element. The X-axis extends
perpendicular to the Y-axis and the Z-axis.
It is also acceptable if an aperture exists between the first
reflective surface and the last reflective surface struck by the
axial main light beam.
It is also acceptable if the aperture is constructed integrally
with a reflective surface.
It is also acceptable if, when the length of the aperture extending
in the main scanning direction is SY and the length thereof
extending in the sub scanning direction is SX, the relationship
expressed by the condition SY>SX is satisfied.
It is also acceptable if the path of the axial main light beam that
first strikes the reflective surface and the path of the axial main
light beam that strikes the imaging element are essentially
perpendicular to each other on the X-Z cross-section.
The invention itself, together with further objects and attendant
advantages, will best be understood by reference to the following
detailed description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a Y-Z cross-sectional view showing a first embodiment
(example 1) of the reading optical system of the present
invention;
FIG. 2 is a X-Z cross-sectional view showing the first embodiment
(example 1) of the reading optical system of the present
invention;
FIG. 3 is a Y-Z cross-sectional view showing a second embodiment
(example 2) of the reading optical system of the present
invention;
FIG. 4 is a X-Z cross-sectional view showing the second embodiment
(example 2) of the reading optical system of the present
invention;
FIG. 5 is a Y-Z cross-sectional view showing a third embodiment
(example 3) of the reading optical system of the present
invention;
FIG. 6 is a X-Z cross-sectional view showing the third embodiment
(example 3) of the reading optical system of the present
invention;
FIG. 7 is a distortion chart for the first embodiment;
FIG. 8 is a distortion chart for the second embodiment; and
FIG. 9 is a distortion chart for the third embodiment.
In the following description, like parts are designated by like
reference numbers throughout the several drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The reflective reading optical system in which the present
invention is implemented is described below with reference to the
drawings. FIG. 1, FIGS. 2 and 3, FIGS. 4 and 5 and FIG. 6 show the
optical constructions and light paths of the first, second and
third embodiments, respectively, using optical cross-sectional
views. In each drawing, 1 is a first reflective surface, 2 is a
second reflective surface, 3 is a third reflective surface, 4 is an
aperture, 5 is an imaging element, and 6 is an axial main light
beam. In a Cartesian coordinate system (X, Y, Z) that has the
surface apex of the first reflective surface (1) as the origin (0,
0, 0), FIGS. 1, 3 and 5 show the Y-Z cross-section, while FIGS. 2,
4 and 6 show the X-Z cross-section.
In each embodiment, the reading optical system comprises first
through third reflective surfaces (1), (2) and (3) only, such that
the image of the original document is formed on the one-dimensional
imaging element (5). Each of the first through third reflective
surfaces (1), (2) and (3) is a free-form surface having a
symmetrical surface relative to the main scanning direction, and
has no symmetrical surface relative to the sub scanning direction.
Here, the main scanning direction is the one-dimensional alignment
direction of the imaging element (5) (i.e., the direction in which
the light receiving elements comprising pixels are aligned), and
the sub scanning direction is the direction that is perpendicular
to the main scanning direction and the plane-normal direction. In
addition, when the light beam that passes through the center of the
original document and the center of the aperture (4) is the axial
main light beam (6), the Z-axis extends along the path of the axial
main light beam (6) that strikes the first reflective surface (1),
the Y-axis extends along the length of the one-dimensional imaging
element (5), and the X-axis extends perpendicular to the Y-axis and
the Z-axis, the reflective surfaces (1), (2) and (3) are positioned
tilted relative to the Y-axis.
In the construction in which multiple reflective surfaces only are
used as the optical surfaces having a focal power, no color
aberration occurs because no transmitting surfaces having a focal
power are included, as in the embodiments. Therefore, even where
the light source used has a wide wavelength range, high contrast
can be obtained. Furthermore, because the absence of color
aberration results in fewer aberrations to control than in the
conventional art, it becomes possible to construct the reading
optical system using fewer surfaces than in the conventional art.
As a result, cost reduction can be attained.
Moreover, by using a free-form surface that has a symmetrical
surface relative to the main scanning direction and no symmetrical
surface relative to the sub scanning direction for at least one of
the multiple reflective surfaces, aberration correction can be
performed for the main scanning direction independent from the sub
scanning direction, and vice versa. In each embodiment, the first
through third reflective surfaces (1), (2) and (3) are arranged
such that they are tilted relative to the Y-axis. When multiple
reflective surfaces are decentered in the X-Z cross-section and the
light beam positions are non-symmetrical in the decenter
cross-section (X-Z cross-section) in this way, good aberration
correction can be obtained by using the above-mentioned
characteristic free-form surface. Therefore, using the reading
optical system of each embodiment in an image reading apparatus
(such as a digital copying machine, a facsimile or a scanner), the
image reading apparatus can be made compact in size, while the cost
is reduced and performance is increased.
In each embodiment, the aperture (4) is integrally formed with the
second reflective surface (2), and the size and shape of the
aperture (4) are determined within the scope of the coating of the
reflective film that comprises the second reflective surface (2).
It is preferred that an aperture (4) exist between the first
reflective surface (1), which the axial main light beam (6) strikes
first, and the last reflective surface (the third reflective
surface (3) in each embodiment), which the axial main light beam
(6) strikes last, as described above. It is further preferred that
the aperture (4) be integrally formed with a reflective surface.
Because each reflective surface (1) through (3) increases in size
as its distance from the aperture (4) increases, if the aperture
(4) is integrally formed with the second reflective surface (2),
the second reflective surface (2) as well as the first and third
reflective surfaces (1) and (3) can be made smaller. As a result,
the entire reading optical system can be made compact. In addition,
where the length of the aperture (4) that extends in the main
scanning direction is SY and the length thereof that extends in the
sub scanning direction is SX, it is preferred that the relationship
expressed by the condition SY>SX be met. Unless this
relationship is met, each reflective surface (1), (2) and (3)
increases in size in the second scanning direction, resulting in a
larger reading optical system as a whole.
It is preferred that the path of the axial main light beam (6) that
strikes the first reflective surface (1) and the path of the axial
main light beam (6) that strikes the imaging element (5) run
essentially perpendicular to each other on the X-Z cross-section,
as in the first embodiment shown in FIG. 2. Because the path of the
axial main light beam (6) that strikes the first reflective surface
(1) extends along the Z-axis, the axial main light beam (6) that
strikes the imaging element (5) should extend essentially along the
X-axis. By having such a light path arrangement, the entire reading
optical system can be made compact (particularly along the
X-axis).
Reflective reading optical systems in which the present invention
is implemented are more specifically described below with reference
to construction data and the like. The examples 1 through 3
referred to here respectively correspond to the first through third
embodiments described above. The light paths and optical
constructions of the examples 1 through 3 are as shown in the
optical cross-sectional views for the corresponding embodiments,
respectively (FIG. 1, FIGS. 2 and 3, FIGS. 4 and 5, FIG. 6). Table
1 shows the construction data for the examples 1 through 3, and
Table 2 shows the shape and size, i.e., the lengths (SX) and (SY),
of the aperture (4) used in the examples 1 through 3, respectively.
The surface configurations of the first through third reflective
surfaces (1), (2) and (3) are shown as free-form surface data
(free-form surfaces 1 through 3), and the arrangements of the first
through third reflective surfaces (1), (2) and (3) and the image
surface (5) are shown as coordinate data (decrntering 1 through 4).
Furthermore, FIGS. 7 through 9 show the distortion for the examples
1 through 3, respectively. In the distortion charts, the horizontal
axis represents the distortion (DISTORTION, %), and the vertical
axis represents the object height (OBJ-HT, mm).
The first through third reflective surfaces (1), (2) and (3) are
free-form surfaces that each have a symmetrical surface relative to
the main scanning direction and no symmetrical surface relative to
the sub scanning direction. The shape of each reflective surface is
expressed by the following formula (FS) that expresses the
displacement amount (sag) along the Z-axis from the X-Y plane. The
free-form surface data for each reflective surface (1), (2) and (3)
comprises the constants in the formula (FS). Where all of the
constants for odd-number Y terms are made 0, the surface can have a
symmetrical surface relative to the main scanning direction (along
the Y-axis).
(FS):Z=C2X+C3Y+C4X.sup.2 +C5XY+C6Y.sup.2 +C7X.sup.3 +C8X.sup.2
Y+C9XY.sup.2 +C10Y.sup.3 +C11X.sup.4 +C12X.sup.3 Y+C13X.sup.2
Y.sup.2 +C14XY.sup.3 +C15Y.sup.4 +C16X.sup.5 +C17X.sup.4
Y+C18X.sup.3 Y.sup.2 +C19X.sup.2 Y.sup.3 +C20XY.sup.4 +C21Y.sup.5
+C22X.sup.6 +C23X.sup.5 Y+C24X.sup.4 Y.sup.2 +C25X.sup.3 Y.sup.3
+C26X.sup.2 Y.sup.4 +C27XY.sup.5 +C28Y.sup.6 + . . . +C35XY.sup.6 +
. . . +C45Y.sup.8 + . . . +C66Y.sup.10
The arrangements of the optical surfaces (1) through (5) are
specified by the position and tilt of the surface. The position of
each surface (1) through (5) is expressed by the coordinates (XDE,
YDE, ZDE) of the point (surface apex) at which the surface crosses
the axial main light beam (6) in the Cartesian coordinate system
(X, Y, Z) that has the surface apex of the first reflective surface
(1) as its origin (0, 0, 0) (unit of measurement: mm). The tilt of
each surface (1) through (5) is expressed by the tilt amount (ADE,
BDE, CDE) relative to the X-axis, the Y-axis and the Z-axis with
the X-Y plane as the reference and the point that the surface
crosses with the axial main light beam (6) as the center (unit of
measurement: .degree.). The coordinate data that expresses the
arrangement of each surface comprises the surface apex coordinates
(XDE, YDE, ZDE) and the tilt amount (ADE, BDE, CDE).
TABLE 1 examples 1 through 3 surface surface surface configuration
distance arrangement object surface radius of curvature = (original
document .infin. surface) reflective surface 1 free-form surfaces 1
450 mm decentering 1 reflective surface 2 (4) free-form surfaces 2
-- decentering 2 reflective surface 3 free-form surfaces 3 --
decentering 3 image surface (5) radius of curvature = --
decentering 4 .infin.
TABLE 2 size of aperture (mm) shape of aperture SX SY example 1
rectangle 4.8 5.5 example 2 rectangle 4.5 5.0 example 3 oval 4.7
5.2
Free-Form Surface Data of Example 1
[Free-Form Surface 1] C4=-1.8800.times.10.sup.-3,
C6=-2.0075.times.10.sup.-3, C7=5.0822.times.10.sup.-6,
C9=2.2652.times.10.sup.-6, C13=-1.7967.times.10.sup.-8,
C15=2.8716.times.10.sup.-7, C18=-6.5560.times.10.sup.-9,
C20=-6.7910.times.10.sup.-9, C26=1.2564.times.10.sup.-10,
C28=-5.2480.times.10.sup.-11, C35=1.7660.times.10.sup.-12
[Free-Form Surface 2] C4=1.7970.times.10.sup.-3,
C6=1.9513.times.10.sup.-3, C7=1.1758.times.10.sup.-5,
C9=-1.3496.times.10.sup.-5, C13=-1.0000.times.10.sup.-6,
C15=2.6659.times.10.sup.-7, C18=-3.8217.times.10.sup.-8,
C20=-3.5279.times.10.sup.-8, C26=-1.7119.times.10.sup.-9,
C28=1.0014.times.10.sup.-8, C35=5.0394.times.10.sup.-10,
C45=-2.1355.times.10.sup.-10
[Free-Form Surface 3] C4=-3.7729.times.10.sup.-3,
C6=-3.9980.times.10.sup.-3, C7=4.5181.times.10.sup.-5,
C9=-5.7685.times.10.sup.-5, C13=-4.5244.times.10.sup.-6,
C15=6.8451.times.10.sup.-7, C20=8.1490.times.10.sup.-9,
C26=1.0567.times.10.sup.-9, C28=1.3911.times.10.sup.-9,
C35=4.5520.times.10.sup.-12, C45=-8.8066.times.10.sup.-12,
C66=1.8875.times.10.sup.-14
Coordinate data of example 1
[Decentering 1] (XDE, YDE, ZDE) = (0, 0, 0) (ADE, BDE, CDE) = (0,
-15, 0) [Decentering 2] (XDE, YDE, ZDE) = (-14.500, 0, -25.115)
(ADE, BDE, CDE) = (0, -40, 0) [Decentering 3] (XDE, YDE, ZDE) =
(8.481, 0, -5.831) (ADE, BDE, CDE) = (0, -70, 0) [Decentering 4]
(XDE, YDE, ZDE) = (-16.519, 0, -5.831) (ADE, BDE, CDE) = (0, -90,
0)
Free-Form Surface Data of Example 2
[Free-Form Surface 1] C4=-1.8911.times.10.sup.-3,
C6=-2.1536.times.10.sup.-3, C7=-2.7027.times.10.sup.-6,
C9=2.1214.times.10.sup.-5, C13=-2.0636.times.10.sup.-7,
C15=1.6858.times.10.sup.-7, C18=2.3722.times.10.sup.-9,
C20=-1.5820.times.10.sup.-9, C26=-6.1970.times.10.sup.-12,
C28=-1.3454.times.10.sup.-11
[Free-Form Surface 2] C4=2.0566.times.10.sup.-3,
C6=2.3899.times.10.sup.-3, C7=-1.3425.times.10.sup.-5,
C9=1.1730.times.10.sup.-5, C13=-1.1533.times.10.sup.-6,
C15=6.5814.times.10.sup.-8, C18=8.4242.times.10.sup.-9,
C20=-1.5402.times.10.sup.-8
[Free-Form Surface 3] C4=-5.3814.times.10.sup.-3,
C6=-5.6662.times.10.sup.-3, C7=1.1956.times.10.sup.-4,
C9=-1.2903.times.10.sup.-4, C13=-1.0131.times.10.sup.-5,
C15=5.8077.times.10.sup.-7, C18=4.7498.times.10.sup.-8,
C20=8.3163.times.10.sup.-9, C26=-1.1219.times.10.sup.-9,
C28=2.2302.times.10.sup.-10
Coordinate data of example 2
[Decentering 1] (XDE, YDE, ZDE) = (0, 0, 0) (ADE, BDE, CDE) = (0,
-20, 0) [Decentering 2] (XDE, YDE, ZDE) = (-22.675, 0, -27.023)
(ADE, BDE, CDE) = (0, -20, 0) [Decentering 3] (XDE, YDE, ZDE) =
(-22.675, 0, 8.029) (ADE, BDE, CDE) = (0, -20, 0) [Decentering 4]
(XDE, YDE, ZDE) = (-33.421, 0, -4.778) (ADE, BDE, CDE) = (0, -40,
0)
Free-Form Surface Data of Example 3
[Free-Form Surface 1] C4=-1.8080.times.10.sup.-3,
C6=-1.3365.times.10.sup.-3, C7=-6.2144.times.10.sup.-6,
C9=-1.1576.times.10.sup.-5, C13=-1.1253.times.10.sup.-7,
C15=2.0092.times.10.sup.-7, C18=9.7911.times.10.sup.-1,
C20=2.6654.times.10.sup.-9, C26=9.1111.times.10.sup.-12,
C28=-1.1949.times.10.sup.-11
[Free-Form Surface 2] C4=1.9879.times.10.sup.-3,
C6=3.0469.times.10.sup.-3, C7=6.9051.times.10.sup.-6,
C9=-3.7952.times.10.sup.-5, C11=-1.9945.times.10.sup.-7,
C13=-6.4193.times.10.sup.-7, C15=1.8502.times.10.sup.-7,
C18=5.7722.times.10.sup.-9, C20=1.2189.times.10.sup.-8
[Free-form surface 3] C4=-5.1014.times.10.sup.-3,
C6=-4.4448.times.10.sup.-3, C7=3.0126.times.10.sup.-4,
C9=-1.3255.times.10.sup.-4, C13=-9.0174.times.10.sup.-6,
C15=1.0060.times.10.sup.-6, C18=-1.7298.times.10.sup.-7,
C20=9.6014.times.10.sup.-9, C26=1.9153.times.10.sup.-9,
C28=1.3052.times.10.sup.-11, C45=4.9348.times.10.sup.-13
Coordinate data of example 3
[Decentering 1] (XDE, YDE, ZDE) = (0, 0, 0) (ADE, BDE, CDE) = (0,
12, 0) [Decentering 2] (XDE, YDE, ZDE) = (14.236, 0, -31.974) (ADE,
BDE, CDE) = (0, 34, 0) [Decentering 3] (XDE, YDE, ZDE) = (-12.856,
0, -3.920) (ADE, BDE, CDE) = (0, 22, 0) [Decentering 4] (XDE, YDE,
ZDE) = (-12.856, 0, -22.168) (ADE, BDE, CDE) = (0, 0, 0)
As described above, using the reading optical system of the present
invention, because no transmitting surfaces are included as optical
surfaces having a focal power, even if the light source used has a
wide wavelength range, high contrast can be obtained. Moreover,
because characteristic free-form surfaces are used, even if the
reflective surfaces are decentered, good aberration correction can
be realized. Where the reading optical system of the present
invention is used in an image reading apparatus such as a digital
copying machine, a facsimile or a scanner, the image reading
apparatus can be made compact, and offer low cost and good
performance.
Although the present invention has been fully described by way of
examples with reference to the accompanying drawings, it is to be
noted that various changes and modifications will be apparent to
those skilled in the art. Therefore, unless such changes and
modification depart from the scope of the present invention, they
should be construed as being included therein.
* * * * *